Refurbishment of a used in‐vacuum undulator from the National Synchrotron Light Source for the National Synchrotron Light Source‐II ring

The National Synchrotron Light Source (NSLS) ceased operation in September 2014 and was succeeded by NSLS‐II. There were four in‐vacuum undulators (IVUs) in operation at NSLS. The most recently constructed IVU for NSLS was the mini‐gap undulator (MGU‐X25, to be renamed IVU18 for NSLS‐II), which was constructed in 2006. This device was selected to be reused for the New York Structural Biology Consortium Microdiffraction beamline at NSLS‐II. At the time of construction, IVU18 was a state‐of‐the‐art undulator designed to be operated as a cryogenic permanent‐magnet undulator. Due to the more stringent field quality and impedance requirements of the NSLS‐II ring, the transition region was redesigned. The control system was also updated to NSLS‐II specifications. This paper reports the details of the IVU18 refurbishment activities including additional magnetic measurement and tuning.     

嵌段共聚物的临界条件液相色谱分离与表征

嵌段共聚物是由两种或两种以上不同性质的聚合物链段通过共价键连接形成的特殊聚合物。它可以结合构成嵌段的不同种类聚合物的性质,得到性能比较优越的功能性聚合物材料,因此越来越受到人们的重视。然而,嵌段共聚物的分离和表征一直都是一项颇具挑战性的工作。临界条件液相色谱（liquid chromatography at the critical condition,LCCC）作为一种新型的液相色谱分离技术,可以使嵌段共聚物中的某种嵌段处于“色谱不可见”（chromatographic invisible）状态,不会影响整个聚合物的保留时间,从而根据嵌段共聚物中其他嵌段长度来分离嵌段共聚物。本文介绍了LCCC分离法的分离原理与实现途径,较为系统地综述了LCCC分离表征嵌段共聚物的近期研究进展,并对该方法目前存在的问题及今后发展前景进行了探讨。     

Orbit matrices of Hadamard matrices and related codes

In this paper we introduce the notion of orbit matrices of Hadamard matrices with respect to their permutation automorphism groups and show that under certain conditions these orbit matrices yield self-orthogonal codes. As a case study, we construct codes from orbit matrices of some Paley type I and Paley type II Hadamard matrices. In addition, we construct four new symmetric (100,45,20) designs which correspond to regular Hadamard matrices, and construct codes from their orbit matrices. The codes constructed include optimal, near-optimal self-orthogonal and self-dual codes, over finite fields and over ${\mathbb{Z}}_4$.     

Statistical methods for network surveillance

The term network surveillance is defined in general terms and illustrated with many examples. Statistical methodologies that can be used as tools for network surveillance are discussed. Details for 3 illustrative examples that address network security, surveillance for data network failures, and surveillance of email traffic flows are presented. Some open areas of research are identified.     

铌酸锂晶体紫外激光诱导畴反转实验研究

报道了在铌酸锂晶体中实现紫外激光诱导畴反转的实验。在一定外加均匀电场下,铌酸锂晶体中通过波长365nm的紫外激光,由于紫外光的照射降低了矫顽电场只在通光区实现畴反转。研究表明,该方案可用于周期性极化铌酸锂的制备,并有望成为制作精细周期性畴结构的有效技术方案。     

Effect of environmental weathering on flexural creep behavior of long fiber-reinforced thermoplastic composites

Flexural creep behavior of nylon 6/6 (NY66)- and polypropylene (PP)- based long fiber (l/d = 2000−10 000) thermoplastic (LFT) composites was investigated as a function of ultraviolet irradiation and moisture absorption. Extrusion/compression-molded panels were prepared according to ASTM D-2990 and conditioned according to ASTM D-618. NY66 and PP LFTs were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Fourier-transform infrared (FTIR) spectroscopy in the unexposed condition, and as-exposed to 253.7 nm UV radiation. The creep compliance of PP LFT increased with increasing UV exposure, whereas the creep compliance of NY66 LFT showed a moderate decrease with increasing UV exposure. Moisture absorption experiments were performed in boiling water until saturation on NY66 and its LFT composites. Characterization of desorbed moisture absorption specimens suggested slight variation in the structure, and an analysis of creep compliances showed minimal changes as compared to the dry/unexposed specimens.     

Liquid chromatography-tandem mass spectrometry for the identification of L-tetrahydropalmatine metabolites in Penicillium janthinellum and rats

L-tetrahydropalmatine (L-THP) is an active alkaloid from Stephania ainiaca Diels. In order to compare the similarities and differences of microbial and mammalian metabolisms of L-THP, the microbial transformation by Penicillium janthinellum and metabolism in rats were investigated. Biotransformation of L-THP by Penicillium janthinellum AS 3.510 resulted in the formation of three metabolites. Their structures were identified as L-corydalmine, L-corypalmine and 9-O-desmethyl-L-THP, respectively, by comprehensive nuclear magnetic resonance and mass spectrometry (MS) analysis. Six metabolites (M1-M6) were detected from the in vivo study in rats and three of which (L-corydalmine, L-corypalmine and 9-O-desmethyl-L-THP) were identified as the same compounds as those obtained from microbial metabolism by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis and comparison with reference standards obtained from microbial metabolism. The structures of the additional three metabolites were tentatively deduced as 2-O-desmethyl-L-THP and two di-O-demethylated L-THP by LC-MS/MS analysis. Time courses of microbial and rat metabolisms of L-THP were also investigated.     

Electronic and geometric characterization of the L-cysteine paired-row phase on Au(110)

We have studied the vapor-phase deposition of L-cysteine on the Au(110) surface by means of synchrotron-based techniques. Relying on a comparison with previous X-ray photoemission analysis, we have assigned the fine structure of the C K-shell X-ray absorption spectra to the nonequivalent carbon bonds within the molecule. In particular, the C1s --> sigma* transition, where the sigma* state is mainly localized on the C-S bond, is shifted well below the ionization threshold, at approximately -5 eV from the characteristic pi* transition line related to carboxylic group. From the polarization dependence of the absorption spectra in the monolayer coverage range, the molecules are found to lay flat on the surface with both the C-S bond and the carboxylic group almost parallel to the surface. We performed in situ complementary surface X-ray diffraction, SXRD, measurements to probe the rearrangement of the Au atoms beneath the L-cysteine molecules. Since the early stage of deposition, L-cysteine domains are formed which display an intermediate fourfold symmetry along [001]. The self-assembly of molecules into paired rows, extending along the [1(-)10] direction, is fully compatible with our observations, as has been reported for the case of D-cysteine molecules grown on Au(110) [Kühnle, A. et al. Phys. Rev. Lett. 2004, 93, 086101.]     

Latent class analysis variable selection

We propose a method for selecting variables in latent class analysis, which is the most common model-based clustering method for discrete data. The method assesses a variable’s usefulness for clustering by comparing two models, given the clustering variables already selected. In one model the variable contributes information about cluster allocation beyond that contained in the already selected variables, and in the other model it does not. A headlong search algorithm is used to explore the model space and select clustering variables. In simulated datasets we found that the method selected the correct clustering variables, and also led to improvements in classification performance and in accuracy of the choice of the number of classes. In two real datasets, our method discovered the same group structure with fewer variables. In a dataset from the International HapMap Project consisting of 639 single nucleotide polymorphisms (SNPs) from 210 members of different groups, our method discovered the same group structure with a much smaller number of SNPs.